Lubricants containing carbodiimides as antioxidants



United States Patent ()fiice 3,346,496 Patented Oct. 10, 1967 Thepresent invention relates to lubricant additives; more particularly itconcerns lubricant additives which consist essentially of carbodiimides.

The carbodiimides to be used as lubricant additives may be monoorpoly-carbodiimides and may belong to the aliphatic, cycloaliphatic oraromatic series. Examples of monocarbodiimides are the following:di-isopropyl-carbodiimide, di-n-butyl-carbodiimide,methyl-tert.-butyl-carbodiimide, dicyclohexyl carbodiimide,diphenyl-carbodiimide, di-p-tolyl-carbodiimide and4,4'-didodecyl-diphenyl-carbodiimide. Of special advantage arediphenyl-monocarbodiimides which carry in the phenyl radicals inorthoposition to the carbodiimide group substituents, e.g. alkyl,alkoxy, aryl and aralkyl radicals, such as 2,2'-diethyl-diphenylcarbodiimide, 2,2'-di-is0propyl-diphenylcarbodiimide,2,2'-diethoxy-diphenyl-carbodiimide, 2,'6,2,6-tetraethyl'cliphenyl-carbodiimide, 2,6,2',6'-tetraisopropyl-diphenyl-carbodiimide,2,6,2,6'-tetraethyl-3,3-dichloro-diphenyl-carbodiimide,2,2-diethyl-6,6'-dichloro-diphenylcarbodiimide,2,6,2,6'-tetra-isobutyl-3,3-dinitro-diphenylcarbodiimide and2,4,6,2',4,6-hexaisopropyl-diphenylcarbodiimide. Suitablepolycarbodiimides are, for example,tetramethylene-w,w'-bis(tert.-butyl-carbodiimide),hexamethylene-w,w'-bis-(tert.-butyl-carbodiimide),tetrarnethylene-w,w'-bis-(phenyl-carbodiimide) and those compounds whichmay be obtained by heating aromatic polyisocyanates such as1,3-di-isOpropyl-phenylene-2,4di-is cyanate,1-methyl-3,5-diethyl-phenylene-2,4-diisocyanate and3,5,3,5-tetra-isopropyl-diphenylmethane-4,4-di-isocyanate, in thepresence of tertiary amines, basically reacting metal compounds,carboxylic acid metal salts or nonbasic organometal compounds at atemperature of at least 120 C., according to the process of GermanPatent No. 1,156,401.

With the aid of carbodiimides it is possible to improve substantiallylubricants of a great variety of types, in particular their resistanceto oxidative attacks. This applies in the first instance to lubricantswhich are produced from mineral oils, but also to lubricating oils ofsynthetic origin which are polyethers or polyether esters, butespecially to lubricating oils based on synthetic polyethers orpolyether esters which contain -(CH O groups alternating several timeswith one another or with other alkyleneO groups and which are describedin German Patent No. 1,071,872. The carbodiimides are, at the same time,also efiective as protective agents against corrosion and are, moreover,capable of keeping the decomposition products formed during thelubricating process in solution. The amounts of carbodiimides requiredin each case can be easily determined in preliminary experiments; ingeneral, additives of 1 to 2 percent by weight, referred to thelubricant, have proved to be sufiicient.

It is noteworthy that the lubricant additives to be used according tothe present invention are compatible with other lubricant additives,e.g. with detergents, agents for increasing the resistance of thelubricating film, and also agents for improving the solidification pointand the viscosity. An especially advantageous embodiment of the presentinvention consists in that the carbodiimides can be added to thelubricants in combination with diphenylamines known as antioxidants,such as 4,4'-di-(methylbenzyl)-diphenylamine, and/ or hydroxyquinolinessuch as S-hydroxyquinoline. Thus, surprisingly, a synergistic effect isachieved. The following examples serve to illustrate the inventionwithout, however, limiting its scope; the parts given are parts byweight.

Example 1 100 parts of a naphthene-basic mineral oil are mixed with 1part of 2,6,2,6'-tetra-is0propyl-diphenyl-carbodiimide. The resistanceof the mineral oil to oxidative attacks is thus substantially improved;the action of the carbodiimide used is further increased by the additionof 0.2 part 4,4'-('dimethyl-benzyl)-diphenylamine and/or8-hydroxyquinoline. This is evident from appropriate comparativeexperiments, the results of which are given in Table I, where theneutralisation numbers (mg. KOH/g. oil) of the oils mixed with thevarious additives are listed after oxidative action.

In the table the letters have the following significance:

A oil without additive B oil with 1% 2,6,2,6'-tetra-isopropyl-diphenyl-carbodiimide C oil with 0.2%4,4'-dimethylbenzyldiphenylamine D oil with 1%2,6,2,6-tetra-isopropyl-diphenyl-carbo-diimide and 0.2%4,4-dimethylbenzyldiphenylamine E oil wit-h 1%2,6,2,6-tetra-isopropyl-diphenyl-carbodiimide and 0.2%8-hydroxyquinoline F oil with 0.2% 4,4-dimethylbenzyldiphenylamine and0.2% 8-hydroxyquinoline G oil with 1%2,6,2',6-tetra-isopropyl-diphenyl-carbodiimide, 0.2%'4,4-dime-thylbenzyldiphenylamine and 0.3% S-hydroxyqumohne.

TABLE I Duration of the N eutralisation numbers oxidative action inhours A B C D E F G The comparative experiments were carried outaccording to the instruction of ASTM-oxidlising test D 943-54: 300 ml.of the oil to be tested were filled, together with 60 ml. distilledwater, into a 60 cm.-high glass cylinder of 4.5 cm. diameter, and ironand copper spirals were introduced into the oil/ water mixture inaccordance with the conditions prevailing in the lubricating processes.Three litres oxygen per hour were then blown at C. through the oil/water mixture via a tube which extended almost to the bottom of the testcylinder. At specified time intervals, 10 ml. of the oil were withdrawnto determine the neutralisation number. When the neutralisation numberreached a value above 2 or when the duration of the oxidative actionamounted to 1000 hours, the test was interrupted.

Example 2 100 parts of a polyether oil obtained according to Example 2of German patent specification No. 1,120,139 by polymerisation of amixture of tetrahydrofuran, ethylene oxide and propylene oxide in thepresence of formaldheydedimethyl acetate and boron trifluoride compoundsof tetrahydrofuran, are mixed with 2 parts of one of the additiveslisted in Table II. It is apparent from the neutralisation numbers giventherein and determined according to the data of Example 1 that theresistance of the oil to oxidative attacks is likewise substantiallyimproved in this way. The letters in the'following table have themeaning:

A oil without additive B oil with 2% di-n-butyl carbodiimide C oil with2% di-cyclohexyl-carbodiimide D oil with 2%,2,6-2,6'-tetraethyl-4,4'-dirnethyl-diphenylcarbodiimide E oil with 2%2,6,2,6-tetraethyl-diphenyl-carbodiimide F oil with 2%2,6,2,6-tetra-isopropyl-diphenyl-carbodiimide TABLE II Duration of theNeutralisation numbers oxidative action in hours A B O D E F 0.00 0.000.01 0.01 0. 03 0. 0. 0O 0. 01 0 01 0. 03 0. 00 0, 00 0.01 0. 01 0.03 0.01 0. 00 0.02 0.01 0. 03 0. 06 O, 00 0. ()2 0. 01 O. 0. 0. 00 0.05 O. 010. 12 0.21 0.03 0. l5 0. 0-1 0. 0. 29 0. 08 0. 34 0.02 0.28 0.38 0.140.58 0.12 0. 3G 0. 48 0.21 0.90 0.30 0. 47 0. 53 0. 29 0.95 0. 54 0. 490.53 0. 39 0.95 0. 84 0. 49

We claim:

1. A lubricating composition comprising (a) an oil base selected fromthe group consisting of a mineral oid and a synthetic polyethercontaining (CH -O- groups and (b) an oxidation-inhibiting amount of amember selected from the group consisting of an aliphaticmonocarbodiimide, aliphatic polycarbodiimide, aromatic monocarbodiimideand aromatic polycarbodiimide.

2. A lubricating composition of claim 1 wherein the carbodiimide is amember selected from the group consisting of di-isopropyl-carbodiimide,di-n-butyl-carbodiimide, methyl-tert.-butyl-carbodiimide,dicyclohexyl-carbodiimide, diphenyl-carbodiimide,di-p-tolyl-carbodiimide, and 4,4-didodecyl-diphenyl-carbodiimide,2,2-diethyl-diphenyl-carbodiirnide, 2,2'-di-isopropyl-diphenylcarbodiimide, 2,2-diethoxy-diphenyl-carbodiimide, 2,6,2,6'-tetraethyldiphenyl carbodiimide, 2,6,2,6-tetraisopropyl-diphenylcarbodiirnide,2,6,2,6'-tetraethyl-3,3-dichloro-dicarbodiirnide,2,6,2,6-tetra-isobutyl-3,3'-dinitro diphenyl-carbodiimide, and2,4,6,2',4',6-hexaisopropyl-diphenylcarbodiimide,tetramethylene-w,w-bis-(tert.-butyl-carbodiimide), hexamethylene-w,w'bis (tert. butyl car-bodiimide tetramethy1ene-w,w'-bis-(phenyl-carbodiimide) 3. A lubricating composition of claim 1 whereinthe carbodiimide is the reaction product of a lower alkyl substitutedphenylene or diphenyl methane diisocyanate in the presence of a memberselected from the group consisting of a tertiary amine, a basicallyreacting metal compound, a carboxylic acid metal salt and a non-basicorgano-metal compound, the reaction being eflected at a temperature ofat least 120 C.

4. A lubricating composition of claim 1 containing an effective amountof an antioxidant selected from the group consisting of diphenylamineand hydroxy quinoline.

5. A lubricating composition of claim 2 containing about l-2%carbodiimide by weight of lubricant.

References Cited UNITED STATES PATENTS 2,298,636 10/1942 Prutton 25251.52,458,526 1/1949 Oberright 252--51.5 2,654,680 1-0/1953 Goppel et al 2609 X 2,776,994 1/1957 Wolfe et al. 252-401 X 2,948,680 8/1960 Fields25251.5 X 3,004,916 10/1961 Ertelt 252- X 3,193,522 7/1965 Neumann et al25250 X 3,193,523 7/1965 Neumann et al. 252401 X DANIEL E. WYMAN,Primary Examiner.

P. P. GARVIN, Assistant Examiner.

1. A LUBRICATING COMPOSITION COMPRISING (A) AN OIL BASE SELECTED FROMTHE GROUP CONSISTING OF A MINERAL OID AND A SYNTHETIC POLYETHERCONTAINING -(CH2)4-O- GROUPS AND (B) AN OXIDATION -INHIBITING AMOUTN OFA MEMBER SELECTED FROM THE GROUP CONSISTING OF AN ALIPHATICMONOCARBONDIIMIDE, ALIPHATIC POLYCARBODIIMIDE, AROMATIC MONOCARBODIIMIDEAND AROMATIC POLYCARBODIIMIDE.